3rd Power DIRTY SINK 6VEL User Manual page 14

Back Panel (Power Tube Biasing):
FAN
CAUTION:
NEVER touch hot tubes!!! Temperatures can exceed 500˚F and cause severe burns!
Biasing your tube amplifier need not be a scary endeavor as the process is pretty straightforward.
Heed all warnings, cautions and instructions and you should do fine. If you're unsure or unclear on
the process, do not attempt to manipulate the bias from factory settings. If, during the biasing
process, you hear a loud "pop" or see a tube "flash" immediately power down the unit and seek a
qualified tube amplifier repair/service technician.
OPERATION NOTES:
• Monitor your output tube bias at idle current. To achieve idle current, your amp must be turned
on and operating at idle (no audio signal being fed into the input or the FX loop return). Make
sure that your speaker is plugged in.
• Attach the negative test lead from your multimeter to the GND- terminal (black) on the back
panel of the amp.
• One at a time, attach the red (positive) test lead from your multimeter to either V8+ or V9+ ter-
minals (red) and note the reading on your meter. Then read the voltage on the other tube. The
resulting numbers should be within 6mv of each other. Note that your maximum bias setting
must be based off of the higher number.
• To optimize your output tube bias, adjust the control screw by inserting a mini flathead screw
driver into control port (see diagram and description for item number (28)). Turn clockwise to
bias your tubes 'hotter' (increasing the idle current) and counter-clockwise to bias your tubes
' c ooler' (decreasing the idle current).
• Cooler settings (lower idle current) can increase the life of your tubes. Too cool and the sound
will tend to be brash and one dimensional.
• Optimal tone and feel can be found when the bias range is around 50% - 70% of your tube's
maximum operating range. This will vary between the types of tubes you choose to operate your
amp with.
• Should you wish to swap to the other set of tubes, you must do so in like-kind pairs as mixed
tubes will not operate correctly and may be hazardous to your amplifier. You can safely substi-
tute either rectifier tube. Again, use caution to mount the correct tubes in the appropriate tube
sockets.
OHM SELECTOR
16Ω
8Ω
14
4Ω